[Ifeffit] charge transfer

Bruce Ravel bravel at bnl.gov
Wed Jan 7 10:23:04 CST 2009


Your questions are of the sort that I always wish the folks working on Feff8 
would volunteer an answer for, but I will do what I can.

> I have another questions. I got the charge transfer of TiO2 from FEFF8 as
> following; Ti: (not absorber)
> Charge transfer :   0.556
>    Electron counts for each orbital momentum:
>       0      0.408
>       1      6.678
>       2      2.350
>       3      0.000
> O:
>  Charge transfer :  -0.280
>    Electron counts for each orbital momentum:
>       0      1.843
>       1      4.354
>       2      0.087
>       3      0.000
> It is known that the electron number of Ti atom ( the atomic number
> 22)&nbs! p;is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^2.

Yes, but Feff8 is just considering the valence electrons.  The core electrons 
are not included in those counts.

> In the results of FEFF, 0 is s orbital, 1 is p orbital so on..  right?

That is correct.  The number in the left column is the angular momentum 
quantum number.

> as you know, there is each s-orbital or p-orbital in principal quantum
> number. which orbital momentum of principle quantum number does 0, 1, 2 and
> 3 mean? 

To the best of my knowledge, Feff8 does not make that clear.  For most 
elements, it considers the valence electrons of a particular angular momentum 
to be the highest lying ones.  See the subroutine corval contained in the 
file POT/corval.f in the Feff8 source tree for more details.

> second
> I cant understand electron counts.
> I thought that Charge transfer was calculated by electron counts for each
> orbital momentum, comparing the electron counts of free atom. So I tried to
> calculate like this:
> In free oxygen atom case, 2^s has 2 electron, 2^p has 4 electron.  
> The electron counts calculated by FEFF8 is 1.843 + 4.354 + 0.087 =6.284
> So charge transfer is 6 - 6.284 = 0.284
> The charge thransfer, 0.284, obtained from my calculation is different from
> the value of FEFF8. 
> How can I get charge transfer form electron counts?

I think the problem is that you are not considering the stoichiometry (or the 
relative number of Ti and O atoms used in the calculation (see 
otherwise it is determined from the contents of the cluster).



 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
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